Direct-positive silver halide emulsion containing a cyanine dye having a pyrazolo(1,5-a)benzimidazole nucleus

ABSTRACT

Direct positive silver halide emulsions sensitized by a cyanine dye in which the carbon atom at the 3-position of the pyrazolo(1,5-a)benzimidazole nucleus is joined by a methine chain to the 2-position or the 4-position of the cyanine heterocyclic nucleus, linkage to the 4-position being, however, only when the cyanine heterocyclic nucleus is a quinoline nucleus or a pyridine nucleus.

United States Patent Sato et al. 1451 Dec. 9, 1975 [54] FOGGED, DIRECT-POSITIVE SILVER [56] References Cited HALIDE EMULSION CONTAINING UNITED STATES PATENTS A CYANINE DYE HAVING A 3,758,309 9/1973 Bailey et al. 96/136 PYRAZOLOU .S-alBENZIMIDAZOLE NUCLEUS Inventors: Akira Sato; Keisuke Shiba; Masanao Hinnta, all of Kanagawa, Japan Assignee: Fuji Photofilm Co., Ltd.,

Minami-ashigara, Japan Filed: Apr. 16, 1973 Appl. No.2 351,386

Foreign Application Priority Data Apr. 14, 1972 Japan 47-37445 US. Cl. 96/101; 96/107; 96/108;

96/130; 260/240 E lnt. Cl. G03C 1/36; G03C 1/28 Field at Search 96/101, 107-108,

Primary ExaminerWon H. Louie, Jr. Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT 29 Claims, N0 Drawings 1 FOGGED, DIRECT-POSITIVE SILVER HALIDE EMULSION CONTAINING A CYANINE DYE HAVING A PYRAZOLO[1,5-a]BENZIMIDAZOLE NUCLEUS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to photographic silver halide emulsions, more particularly, it relates to a direct positive silver halide emulsion sensitized by a dye having a novel pyrazoloi 1,5-albenzimidazole nucleus.

2. Description of the Prior Art When a silver halide photographic material is exposed to light containing wave lengths in the sensitive wave length region of the photographic material and then developed, the blackened density thereof increases with increased exposure amounts up to a maximum value, but if the exposure amount further increases the blackened density again reduces. This phenomenon is generally called solarization.

Also, in a silver halide photographic material having a silver halide emulsion layer which has been optically or chemically fogged during the production of the silver halide emulsion, a reversal effect similar to that in solarization, namely the phenomenon that the blackened density again decreases as the exposure increases, is observed. By utilizing such a phenomena, positive images can be obtained.

The term direct positive silver halide emulsion" in this specification means a silver halide emulsion prepared such that it directly forms a positive image after ordinary exposure to light, i.e., positive light image development.

As sensitizers for ordinary negative silver halide emulsions there are known many dyes such as monomethinecyanine dyes, trimethinecyanine dyes, merocyanine dyes and rhodacyanine dyes. However, the use of these dyes for the sensitization of direct positive silver halide emulsions is frequently accompanied with disadvantages, for instance, softening or flattening of characteristic curves and re-reversal (the phenomenon that with an increase in the exposure amount the blackened density decreases and then the blackened density increases again).

Also, dyes conventionally known as sensitizers for direct positive silver halide emulsions frequently have faults such as leaving color stains after processing of photographic silver halide materials containing them. The formation of such color stains is particularly inconvenient for color photographic papers. When such dyes are used as sensitizers high whiteness is not obtained in black and white photographic papers and further true color reproduction cannot be obtained in color photographic papers. Furthermore, the formation of such color stains is particularly undesirable in hard or high contrast photographic materials used for lithographic films, X-ray photographic films, duplication films for microphotographs, etc.

The dyes used for the sensitization of direct positive silver halide emulsions should not exhibit the above faults and further should not reduce the maximum density of the images formed.

SUMMARY OF THE INVENTION An object of this invention is, therefore, to provide a direct positive silver halide emulsion of high sensitivity, desired maximum image density and further giving substantially no color stains.

2 As the result of intensive investigations to reach the above-indicated object, the inventors succeeded in reaching the present invention.

That is to say, the invention provides a direct positive 5 silver halide emulsion containing at least one cyanine being, however, only when the cyanine heterocyclic nucleus is a quinoline nucleus or a pyridine nucleus.

ln this specification the manner of numbering the substituted positions of the cyanine nucleus of the cyanine dye used in this invention is such that the position of the nitrogen atom is designated as l.

DETAlLED DESCRIPTION OF THE lNVENTlON Specific examples of the cyanine heterocyclic nu cleus of the cyanine dye used in this invention include an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthothiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, 21 naphthoselenazole nucleus, a 2-pyridine nucleus, a 4-pyridine nucleus, a Z-quinoline nucleus, a 4quinoline nucleus, a 3-isoquinoline nucleus, a l-isoquir ioline nucleus, an imidazole nucleus, :1 benzimidazole nucleus, an indolenine nucleus, an imidazo[4,5-b]quinoxaline nucleus, a pyrrolidine nucleus and the like. The benzene rings of those heterocyclic rings and/or the condensed heterocyclic rings may have substituents Examples of the substituents are an alkyl group, an aryl group, a hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, a nitro group, and a halogen atom, with preferred alkyl groups or moieties having l-20 carbon atoms, preferred alkoxy groups having 1 10 carbon atoms and a preferred aryl group being a phenyl group.

As examples of such cyanine nuclei, there are thiazoles such as thiazole, 4-methylthiazole, 4phenylthiazole, 4-(p-hydroxyphenyl)thiazole, Smethylthiazole, S-phenylthiazole, S-(o-hydroxyphen yl thiazole, 4,5-dimethylthiazole and 4,5-diphenylthiazole; benzothiazoles such as benzothiazole, 4- hydroxybenzothiazole, 4-fluorobenzothiazole, 4- chlorobenzothiazole 5-chloroben zothiazole, 6- chlorobenzothiazole, 7-chlorobenzothiazole, 4-methylbenzothiazole, S-methylbenzothiazole, fi-methylbenzothiazole, 5 ,-dimethylbenzothiazole 5 -bromoben zothiazole, 6-bromobenzothiazole, S-phenylbenzothiazole, 6-phenylbenzothiazole, 4-phenylbenzothiazole, 4-methoxybenzothiazole, S-methoxybenzothiazole, 6-methoxybenzothiazole, 7-methoxybenzothiazole, 5-iodobenzothiazole, fi-iodobenzothiazole, S-ethoxybenzothiazole, 4ethoxybenzothiazole, 5- ethoxycarbonylbenzothiazole, tetrahydrobenzothiazole, S-(N,N-dimethylamido)benzothiazole, 5,6-dimethoxybenzothiazole, S-hydroxybenzothiazole, 6- hydroxybenzothiazole, S-nitrobenzothiazole and 5- chloro-6-nitrobenzothiazole; naphthothiazoles such as (ii-naphthothiazole, B-naphthothiazole, Bfimaphthothiazole, 8-methoxy-Bmaphthothiazole, S-ethoxy-B- naphthothiazole, 7-methoxy-a-naphthothiazole, 8- methoxy-til-naphthothiazole, S-hydroxy-B-naphthothiazole, 7-hydroxy-a-naphthothiazole and S-ethyl-B- naphthothiazole; oxazoles such as oxazole, 4-methylox azole, S-methyloxazole, S-phenyloxazole, 4-(p-hydroxyphenyl)oxazole, 4,5-diphenyloxazole, 4-ethyloxazole,

4.5-dimethylxaz0le, 4-phenyloxazole, and S-(mhydroxyphenyhoxazole; benzoxazoles such as benzoxazole, fi-chlorobenzoxazole, S-methylbenzoxazole, phenylbenzoxazole, fi-methylbenzoxazole, 6-nitr0benzoxazole. 5,6-dimethylbenzoxaz0le, 4.6-dimethylbenzoxazole, S-methoxybenzoxazole, S-ethoxybenzoxazole, -chlorobenzoxazole, 6-meth0xybenz0xazole, S-hydroxybenzoxazole and 6-hydroxybenzoxazole; naphthoxazoles such as anaphth0xazole, [LB-naphthoxazole, B-naphthoxazole (-hydroxy-Bnaphthoxazole); selenazoles such as selenazole, 4-methylselenazole, 4-phenylselenaz0le and 4-(p-hydroxyphenyl) selenazole; benzoselenazoles such as benzoselenazole', 5-chlorobenz0selenaz0le, S-methoxybenzoselenazole, S-hydroxybenzoselenazole and tetrahydroxybenzoselenazole; naphthoselenazoles such as anaphthoselenazole, B,B-naphth0selenazole, B-naphthoselenazole and 7-hydroxy-B-naphthoselenazole; thi' azolines such as thiazoline, 4-methylthiazoline, and 4- (p hydroxyphenyl)thiaz0line; 2-quin0lines such as 2- quinoline, 3-methyl-2-quin0line, S-methyl-Z-quinoline, 7-methyl-2-quinoline, S-methyl-Z-quinoline, 6-chl0ro- 2-quinoline, 8-chlor0-2-quin0line, 8-fluoro-2-quin0- line, 6meth0xy-2-quin0line, 6-eth0xy-2-quinoline, 6- hydroxy-Z-quinoline, 7-hydroxy-2-quin0line and 8- hydroxy-2-quin0line', 4-quin0lines such as 4-quinoline, 5-methoxy-4-quin0line, 6-methoxy-4-quinoline, 7- methoxy-4-quinoline, 8-methoxy-4-quinoline, 6-methyl-4-quinoline, 7-chloro-4-quin0line and S-trifluoromethyl-4-quinoline; isoquinolines such as isoquinoline, B-methylisoquinoline, S-methylisoquinoline, 7-methylisoquinoline, fi-chloroisoquinoline, 6-methox yisoquinoline and B-methoxyisoquinoline; 1-

Formula I nitroindolenine; Z-pyridines such as pyridine, 4-methylpyridine, -methylpyridine, 4,6-dimethylpyridine, 4- butylpyridine, 4-decylpyridine, 4-octadecylpyridine, 4,6-dibutylpyridine, 4-benzylpyridine, 4-phenylpyridine, 4-(p-hydr0xyphenyl)pyridine, 4,6-diphenylpyridine, 4,6-dinaphthylpyridine, 4-chloropyridine, 4- bromopyridine, 4,6-dichloropyridine, 4-chl0ropyridine, -bromopyridine, 4-hydr0xypyridine, 4-meth0xypyridine, 4-ethoxypyridine, 6-methoxypyridine, 6- ethoxypyridine and 4,6-dimeth0xypyridine; 4-pyridines such as pyridine, Z-methyIpyridine, 2-butylpyridine, 2- decylpyridine, 2-octadecylpyridine, 2,6-dimethylpyridine, 2,6-dibutylpyridine, 2-benzylpyridine, Z-phenylpyridine, Z-(p-hydroxyphenyl)pyridine, 2,6-diphenylpyridine, 2-chl0r0pyridine, 2-br0mopyridine, 2,6- dichloropyridine, 2-hydr0xypyridine, Z-methoxypyridine, 2-ethoxypyridine and 2,6-dimeth0xypyridine; imidazo( 4,S-b)-quinoxalines such as l ,3-diethylimidazo-(4,5-b)-quinoxaline, 1,3-diethyl-6-nitr0- imidazo(4,5-b)-quin0xaline, l,3-diphenylimidazo-(4,5- b)-quinoxaline, 6-chl0rol ,3-diphenylimidazo-(4,5-b)- quinoxaline, 1,3-diallylirnidazo(4,5-b)-quin0xaline and ,3-dicyclohexylimidazo-( 4,5-b)-quinoxaline; oxaline and benzimidazoles such as benzimidazole, 5,6- dichlorobenzimidazole, l -ethyl-5-nitr0benzimidazole and l-ethyl-5,-dichlorobenzimidazole, l-ethyl-S- methoxycarbony]benzimidazole, etc.

Among those cayanine heterocyclic nuclei, benzothiazoles, benzoselenazoles, 2-quin0lines and 4-quin0 lines are particularly preferred.

Examples of preferred cyanine dyes used in the present invention can be shown by the following general formulae I and II.

Formula ll ll (1 N1 In the above formulae l and ll, R and R each represents an unsubstituted alkyl (C,C group such as a methyl group,

* the brackets in parentheses indicate preferred carbon atoms in the alkyl moiety an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an n-pentyl group and an n-hexyl group; a hydroxyalkyl (C -C group such as a B-hydroxyethyl group and a y-hydroxypropyl group; an acetoxyalkyl (C -C group such as a B-acetoxyethyl group, and a y-acetoxyprop'yl group; an alkoxyalkyl (C -C group such as a B-methoxyethyl group and a y-methoxypropyl group; a carboxyalkyl (C -C group such as a B-carboxyethyl group, a y-carboxypropyl group, a 'y-carboxybutyl group and a w-carboxypentyl group; an alkoxycarbonylalkyl (C -C group such as a B-methoxycarbonylethyl group and a *y-ethoxycarbonylpropyl group; a sulfoalkyl (C C group such as a B-sulfoethyl group, a 'y-sulfobutyl group and a y-sulfobutyl group; an analkyl group such as a benzyl group and a phenethyl group; a sulfoaralkyl group such as a p-sulfophenethyl group; a carboxyaralkyl group such as a p-carboxyphenethyl group; or a vinylmethyl group, R represents a group conventionally known as a substituent for a pyrazolo[ l,5-a]benzimidazole compound, such as a hydrogen atom, an alkyl group (e.g., a methyl group, an ethyl group, a propyl group), a benzyl group, a carboxyl group, an alkoxycarbonyl group (e.g., a methoxycarbonyl group and an ethoxycarbonyl group), an amino group, an acylamino group (e.g., an acetylamino group), an aryl group (e.g., a phenyl group and a pmethoxyphenyl group) and an acid amide group, L and L; each represents a methine chain such as --CH= and CR5 (wherein R represents an alkyl group or alkoxyalkyl group such as a methyl group an ethyl group, or an ethoxyethyl group or an aryl group such as a phenyl group), and L and R may combine with each other via a methylene chain, e.g., to form a 5 or 6 membered cyclic ring, Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus, such as, practically speaking, those mentioned above, R represents a group conventionally known as a substituent for a pyrazolo[ l,5-a]benzimidazole compound, such as a halogen atom (e.g., a fluorine atom, a chlorine atom and a bromine atom), a lower alkyl group (e.g., a methyl group and an ethyl group), an alkoxyl group (e.g., a methoxy group and an ethoxy group), an aryl group (e.g., a phenyl group), a carboxyl group, an alkoxycarbonyl group (e.g., a methoxycarbonyl group), an acylamino group (e.g., an acetylamino group), n represents or 1, m represents 0, 1 or 2, p represents 1, 2, 3 or 4, and x represents an acid anion such as a chloride ion, a bromide ion, an iodide ion, a thiocyanate ion, a perchloride ion, a p-toluenesulfonate ion, a methylsulfate ion and an ethylsulfate ion.

The cyanine dyes shown by the aforesaid general formula I can be prepared by reacting under heating a compound represented by general formula III Formula II] 6 wherein R R and p have the same significance as in the General formula I and a heterocyclic quaternary ammonium salt represented by the general formula IV wherein Y represents SR, OR", or

COCH;

(wherein R and R" each represents a methyl group, an ethyl group or a phenyl'group) and R Z, L L n, m, and Xhave the same significance as in General formula l in ethanol in the presence of an organic base such as triethylamine.

The cyanine dyes represents by general formula I can also be prepared by reacting a compound represented by general formula V obtained by subjecting the compound of the above-mentioned general formula III to a Vilsmeier reaction Formula V CH3 R -c\L-cEcn-N\cH3 wherein R R and p have the same significance as in general formula I and a heterocyclic quaternary ammonium salt represented by general formula VI wherein R, L,, L X@ 2, m, and n have the same significance as in general formula I in acetic anhydride with heating and then treating the product with an alkali. ln place of reacting the above reactants in acetic anhydride, both reactants may be reacted in nitrobenzene in the presence of an organic base such as triethylamine, while heating, before the alkali treatment.

The dyes represented by general formula ll may be obtained by alkylating a cyanine dye represented by general formula I with an ordinary quaternizing reagent such as dimethyl sulfate, methyl-p-toluene sulfonate, propane sultone, butane sultone and an alkyl halide. In this case, it is possible that the alkylation will occur to the nitrogen atom at the l-position of the pyrazolo[ l ,5- a]benzimidazole nucleus or the nitrogen atom at the 8 wherein R,, R R R Z, L,, L n, m, p, and Xhave the same significance as in the general formula II.

Specific examples of the cyanine dyes used in this invention are illustrated below together with their absorption maximum wave lengths ()t in methanol solution.

CH CH CHCH CH N use l =CHCH CH MeOH l X 535ml N [3 H N CH CH =CH-CH CH lVleOl-l I max 550ml N CH A solution prepared by dropwise adding 1 g of phosphorus oxychloride to 20 ml of dimethylformamide while under ice-cooling is added to a solution of 3 g of Z-methylpyrazolel LS-ahbenzimidazole in 30 ml of dimethylformamide and the mixture is heated for 1 hour on a warm water bath at atmospheric pressure. The reaction product is cooled, added to water, and the solution is neutralized by adding an aqueous solution of sodium carbonate. The crystals precipitated are recov ered by filtration, washed with water and dried to give 2.4 g of the above intermediate product having a mele ing point of 216C.

In the same manner as above, except varying the starting materials, 2-phenyl-3-dimethylaminome thylenepyrazolol LS-al-benzimidazole is also obtained as crystals melting at 235C.

2. Synthesis of dye 2:

Dye2

i. 2 g of 2-acetanilidevinyl-3-ethylbenzothiazoliurn iodide and 1 g of Z-methylpyrazolol l,5-albcnzimidazole are refluxed for 1 hour in 50 ml of etha nol on a warm water bath in the presence of 2 ml of triethylarnine at atmospheric pressure. After cooling. water is added to the reaction product and then the product is extracted with benzene. After drying the benzene solution over anhydrous so dium sulfate, the solution is concentrated and the reaction product is then separated by means of alumina column chromatography. By recrystallizing the product from ethanol, 0.5 g of the Crystals of dye 2 melting at 146C are obtained.

ii. 3.5 g of 3-ethyl 3-methyl-bcnzothii.i1oliuin-ptolnene. sulfonatc and 1.3 g of the Z-methyl3dimethylarninomethylenepyrazolol l ,5-a lbcnzimidazolc prepared by the above synthesis otthe intermediate are refluxed in 100 ml of acetic anhydride for I minutes by heating at atmospheric pressure to conduct the reaction, and then the crystals formed are separated by liltration and dried lllCltl-tttltlltlOll product oi the dye t Z l. The crystals thus obtained are dissolved by heating in methanol and then a small amount. ol aqueous sodium hydroxide solution is added to the solution. whereby crystals are formed. When the crystals are recovered by filtration and recrystallized from ethanol. 4 g of dye. 1 is obtained.

3. Synthesis of dye l8.

0.5 g of dye Z is reacted with l ml of methyl-p-tol uenesulfonute by heating for one minute at atmospheric pressure. Alter cooling the reaction product, the crystals precipitated are recovered washed with ether and dissolved in methanol. Then. an aqueous sodium iodide solution is added to the methanol solution and the crystals precipitated are recovered by liltration, washed with water and dried When the crystals obtained are recrystallized from a mixture of methanol and chloroform. 0.4 g of dye l R melting at 274C is ob tained.

Other dye intermediate products and dyes can easily be prepared in substantially the same manner as above merely by varying the starting materials.

Having thus described the synthesis of representative dyes in accordance with this invention. it is appropriate to describe in greater detail certain preferred embodiments of this invention.

it is preferred that the direct positive silver halide emulsion of this invention contain an organic desensitizer.

The organic desentizer used herein refers to a mate rial having the faculty of catching or trapping l'ree electrons generated in silver halide grains by irradiation and capable olbeing adsorbed on the silver halide. The organic descnsitizer can further be defined as a material having a minimum space electron energy level lower than the electron energy level ol the conductive zone of the silver halide grains. It is preferably a com pound having a maximum occupied electron energy level lower than the valence electron zone of the silver halide grains. l'hc values of these electron energy levels can be determined, although complicated procedures are required for the measurement.

For instance, a practical example ol determining the electron energy levels for simple symnietiic cyanine dyes is reported by Tani and Kiltuchi; Photographic Science and Engineering"; Vol. I l (3 l. l E li l JoTJ and a practical example of determing the electron energy levels for typical merocyanine dyes is reported by Shiba and Kubodera; Presentation No. 3- ll" of the lnternational Congress oi Photographic Science. Will llvloscinv 1.

It is known that these electron energy levels correspond linearly to the. anode polarographic hall" wave potentials (Fox! and the cathode polarographic half wa v potentials Hired) Many of such organic desensitizers as can be used in this invention are described in the specifications of 1. l8.

wherein R represents an alk 1 group or an allyl group,

3 represents 1 or 2, and Z, and m have the same significance as in general formula 1.

Specific examples of R include a methyl group, an ethyl group, a butyl group, a hydroxyalkyl group (e.g.,

a hydroxyethyl group), a carboxyalkyl group (e.g., carboxymethyl group and a B-carboxypropyl group) and a sulfoalkyl group (e.g., a 2-sulfoethyl group and a 4-sulfobutyl group).

Specific examples of organic desensitizers which can be employed in the present invention are, phenosafra- 3 nine, pinakryptol yellow, 5-m-nitrobenzylidenerhoda- -nine, 3-ethyl-5-m-nitrobenzilidene rhodanine, 3-ethyl- 5-(2,4 dinitrobenzilidene) rhodanine, 5o-dinitrobenzilidene-3-phenylrhodanine, l,3-diethyl6-nitrothia-2'- cyanineiodine salt, 4-nitro-6-chlorobenzotriazole, 3,3'-diethyl-6,6-dinitro-9-phenylthiacarbocyanine.io-

dine salt, 2-(p-dimethylaminophenyliminomethyl)benzothiazoleethoethyl. sulfate, crystal violet, 3,3'-diethyl-6,6'-dinitrothiacarbocyanine.ethyl sulfate, 1',3- diethyl-6-nitrothia-2'-cyanine.iodine salt, 1,3-diamino- S-methylphenazinium chloride, 4-nitro-6-chlorobenzotriazole 3 3 -di-p-nitrobenzylthiacarbocyanine bromide 3 ,3 -di-p-nitrophenylthiacarbocyanine. iodine salt, 3 ,3 '-dip-nitrophenylthiacarbocyanine 3 3 dimethyl-9-trifluoromethylthiacarbocyanine.iodine salt, 9-( 2,4-dinitrophenylmercapto)3 ,3 '-diethylthiac arbocyanineiodine salt, bis(4,6-diphenylpyryl-Z-trimethinecyanine.perchlorate, anhydrous 2-p-dimethylaminophenyliminomethyl-6-nitro-3-(4-sulfobutyl)- benzothiazolium. hydroxide, l-(2-benzothiazoly)-2-(pdimethylaminostyryl )-4,6-diphenylpyridinium.iodine salt, l,3-diethyl-5-[ l ,3-neopentylene6-( 1,3,3-trimethyl-2indolinylidene)-2,4-hexadienylidene]-2-thiobarbitun'c acid, 2,3,S-triphenyl-2l-ltetrazolium chloride, 2-( 4-iodophenyl )-3-( 4-nitrophenyl )-5-phenyl-tetrazolium chloride, l-methyl-8-nitroquinolinium methyl sulfate and 3 ,6-bis[ 4-( 3-ethyl-2-benzothiazolinylidene )-2-butenylidene]- l ,2 ,4,5-cyclohexanotetraon.

As silver halide emulsions used in this invention, ()0

there are illustrated a silver chloride emulsion, a silver bromide emulsion, a silver chlorobromide emulsion, a silver chloroiodide emulsion and a silver chloroiodobromide emulsion.

The grain size of such silver halides can be in the gen- ,5

erally used range, but particularly good results are obtained when a silver halide having a mean grain size of 0.05 microns to 1.0 micron is used. Also, the silver halide grains used in this invention can be reglar grains or irregular grains, but the invention is applied more effectively when regular silver halide grains are usedv Furthermore, a simple dispersion type silver halide emulsion or a non-simple dispersion type silver halide emulsion can be used in this invention, but the use of a simple dispersion type emulsion is more preferred.

in general, silver halide emulsions used for direct positive silver halide photographic materials are classitied into the following two types.

The first type is a silver halide emulsion having nuclei capable of trapping free electrons in the silver halide crystals, the surfaces of the silver halide grains of which have been preliminarily fogged chemically. The main feature of the silver halide emulsion of this type is that by the addition of a sensitizing dye or dyes the silver halide emulsion is highly sensitized by the action of spectral sensitization as well as being sensitized in its characteristic absorption region. A silver halide emulsion of this type is required to have its halogen composition adjusted so that the chemical sensitizers or the salts of metals belong to group VIII of the periodic table used for providing free electron trapping nuclei are readily incorporated in the silver halide. Furthermore, by adding an organic desensitizer to the silver halide emulsion, the occurence of clearance and particularly the occurence of re-reversal can be prevented. Still further, by adding bromide ions or iodide ions to a silver halide emulsion of this type the maximum density can be increased, the emulsion can be further sensitized and also the occurence of clearance can be prevented.

Emulsions of this type are described in US. Pat. Nos. 2,401,051, 2,717,833, 2,976,149 and 3,023,102, British Pat. Nos. 707,704, 1,097,999 and 1,520,822, and French Pat. Nos. 1,523,626, 1,520,817 and 1,520,824.

The second type is a silver halide emulsion which has no free electron trapping nuclie in the silver halide, the surfaces of the silver halide grains of which have been chemically fogged. This type of emulsion has crystal defects as low as possible and comprises regular silver halide crystals having no twinning plane, and is prefera- 0 bly pure silver bromide. While this type of silver halide emulsion does not give direct positive images per se, if an organic desensitizer is adsorbed on the silver halide of the emulsion, direct positive images can be obtained.

Emulsions of this type are described in US. Pat. Nos.

5 3,501,306, 3,501,307, 3,501,310 and 3,531,288, British Pat. Nos. 1,186,717, 1,186,714 and 1,186,716, and French Pat. Nos. 1,520,821, 1,520,817, 1,522,354 and 1,520,824.

In the present invention, silver halide emulsions of both types can be employed. In other words, both types of the aforesaid silver halide emulsions can be effectively sensitized by the compound or the cyanine dyes of the present invention.

The silver halide emulsions used in this invention can be fogged by light or chemically. Chemically fogged nuclei are formed by the addition of a reducing organic compound such as a hydrazine derivative, formalin, thiourea dioxide, a polyamine compound, amine borane or methyldichlorosilane and the like as disclosed in Belgian Pat. Nos. 721,564 and 708,563, US. Pat. No. 2,588,982, British Pat. No. 821,251, French Pat. No. 739,755 and Japanes Pat. Publication No. 43-13488.

The fogged nuclei can also be formed, in addition to the aforesaid manner, by the combination of a reducing agent and ions of a metal nobler than silver, such as gold ions, platinum ions or iridium ions or by a combination of such metals and halogen ions, as disclosed in US. Pat. Nos. 2,717,833 and 3,023,102, Belgian Pat. Nos. 713,272 and 721,567 and British Pat. No. 707,704.

In the silver halide emulsion of this invention, gelatin is generally used as the protective colloid, and inert gelatin is particularly preferred. However, instead of gelatin a photographically inert gelatin derivative or watersoluble synthetic polymer such as polyvinyl acrylate, polyvinyl alcohol, polyvinyl pyrrolidone, polyvinyl alginate, carboxymethyl cellulose, and hydroxymethyl cellulose may be used, as may mixtures of any such materials.

The direct positive silver halide emulsions of this invention can further contain, if desired, a stabilizer for the fogged nuclei, such as a mercapto compound, a thion compound or a tetraazaindene compound; an agent to prevent the occurence of clearing (often re ferred to as uncoloring), such as a stilbene compound or an azine compound; a whitening agent; an ultraviolet absorbant; a hardening agent such as chromium alum, a 2,4-dichloro-s-triazine compound, an aziridine compound, an epoxy compound, a mucohalogenic acid compound (e.g., halogen formyl maleic acid compound); a wetting agent such as sodium polyalkylene sulfonate or saponin or an anionic surface active agent having a betaine structure; an antiseptic or disinfectant agent; a plasticizer such as polyalkyl acrylate, a copolymer of an alkylacrylate and acrylic acid or a polyalkylene oxide; or a color coupler.

The amount of the dimethine dye depends upon the amount of the silver halide and the surface area of the silver halide grains in the silver halide emulsion, but good results are obtained when the amount is l X to 2 X 10 mol of dye or dyes per mol of silver halide.

These dye(s) are generally added to the silver halide emulsion as a solutions in a solvent miscible with water, such as methanol, ethanol, ethyleneglycol monomethyl ether, methylethyl ketone, acetone and pyridine, as well as water. Upon dissolving the dye(s) in such a solvent, ultrasonic waves may be applied to the system to promote dissolution. Further, the methods used for the sensitization of negative silver halide emulsions such as the method described in Japanese Pat. Nos. 23,389/l959, 27,555/l969, and 22,948/1969; U.S. Pat. Nos. 3,485,634; 3,342,605; and 2,912,343; and German Patent Application (OLS) No. 1,947,935 may also be employed.

It is convenient to add the dyes to the silver halide emulsion just before coating, but they can be added during chemical ripening of the silver halide emulsions or during precipitation of the silver halide(s).

The amount of the organic desensitizer used in the present invention depends upon the kind of desensitizer, but is preferably 2 X 10 to 10 mol per mol of silver halide.

The silver halide emulsions of this invention can be applied to various supports to give photographic elements. The silver halide emulsions of this invention can be applied to one surface or both surfaces of the support and the support may be transparent or opaque. Typical examples of the supports are cellulose nitrate films, cellulose acetate films, polyvinyl acetal films, polystyrene films, polyethylene terephthalate films, other polyester films, glasses, papers, metallic foils and woods. Plastic-laminated papers can also be used as the support. The exact support chosen is not important.

The photographic silver halide material comprising the silver halide emulsion layer of this invention may be processed after exposure in the manner used for prior art direct positive emulsions, e.g., in separate develop ment, fix, stabilization, etc., baths or in a bath having a combination of such processing functions.

The first feature of the present invention is that the direct positive silver halide emulsion is sensitized by at 30 least one cyanine dye having the pyrazolo[ l,5-a]ben- Zimidazole nucleus. In particular, such alkylated cyanine dyes give higher sensitivity to the silver halide emulsion.

The second feature of the present invention is that a direct positive silver halide emulsion having a sharp spectral sensitization maximum is obtained. In other words, the spectral sensitivity curve of the direct positive silver halide emulsion of this invention has such a form that the longer wave length end of it is sharply cut. Therefore, the photographic materials prepared using the direct positive silver halide emulsions of this invention can be easily handled under a safe light.

The third feature of the present invention is that the cyanine dye (or dyes) having the pyrazolo[ l,5-a]benzimidazole nucleus used in this invention has the excellent property of not substantially reducing the maximum density of the direct positive silver halide emulsion.

The fourth feature of the present invention is that the direct positive silver halide emulsion of this invention shows substantially no reduction in maximum density during storage.

The novel dimethine dyes used in this invention have such excellent features as mentioned above, and further by using the dimethine dyes together with the aforesaid organic desensitizers, the reversal sensitivity of the silver halide emulsions can further be improved and also direct positive silver halide emulsions showing excellent clearance can be prepared.

The direct positive silver halide emulsions of this invention can, of course, be used for making duplicating photographic materials for lithographic films and hard or high contrast direct positive silver halide photographic materials used for duplicating originals as well as for making duplicating photographic materials for microphotographic films and also comparatively soft direct positive silver halide photographic materials such as duplicating photographic materials for X-ray photographs. The direct positive silver halide emulsion can also be used for making color photographic materials.

The direct positive silver halide emulsions of this invention can be used not only for the case of exposure to light, but also for the case of exposure to electrons, X- rays or gamma rays.

Moreover, the dimethine dyes to be used in this invention can be also used as photographic dyes, such as dyes for light-filtering layers, dyes for anti-irradiation and antihalation, etc.

The invention will now be illustrated in more detail by referring to the following several examples.

All percentages are weight percent, unless otherwise indicated.

EXAMPLE 1 The following four solutions were prepared for making silver halide emulsion.

First solution:

inert gelatin 8 g aqueous potassium bormide solution (I normal) 5 cc water (60C) 500 cc. Second solution:

silver nitrate 100 g water (60C) 500 cc. Third solution:

potassium bromide g water (60C) I50 cc. Fourth solution:

inert gelatin g water 300 cc.

While maintaining the system at 60C, the second so lution and the third solution were added to the first solution over a 50 minute period and then the mixture was physically ripened for 5 minutes by permitting it to stand at 60C. Then, 15 cc of a 0.2 normal aqueous potassium iodide solution was added to the ripened mixture and thereafter the pAg of the mixture was adjusted to 6.0 using an aqueous silver nitrate solution. Then, 12 mg hydrazine and 1.0 mg gold chlorine were added to the mixture and after adjusting the pH thereof to ID using aqueous sodium hydroxide solution, the resultant mixture was further ripened for 10 minutes by permitting it to stand at 60C. The mixture was neutralized using citric acid and then was washed with water. The mixture was melted again and the forth solution indi cated above was added thereto to give the silver halide emulsion. The silver halide emulsion thus prepared contained silver halide grains having a mean grain size of about 0.2 microns, the silver halide grains being regular tetragonal system grains having the (100) plane.

A methanol solution of the dimethine dyes as shown in Table l was added to the silver halide emulsion prepared above, and after further adding 40 ml/Kg of emulsion of a 4 wt aqueous solution of saponin, the resultant emulsion was applied to a cellulose triacetate film in a dry thickness of about 5 microns to give a sample photographic material.

The sample was exposed for 1 second through an optical wedge to a tungsten light source of 2854K, developed in the developer having the following composition for 2 minutes at 20C., and then fixed in an acid hardening fix solution.

Composition of the developer:

Metol 3.l g anhydrous sodium sulfite 45 g hydroquinone 12 g sodium carbonate tmono hydrate] 79 g potassium bromide 2 g water added to 1 liter Table 1 Dye (mol density) cc/l g of Sample emulsion Sensitivity Dmax Dmin 1 2.8 2 4 (8 X IO") 16 890 2.7 0.05 3 l9 (8 X 10 I6 I320 2.8 0.06 4 20 (B X I0) 24 I00 2.8 0.06 21 (8 X l0) I6 159 2.8 0.06 6 22 (8 X 32 4790 2.8 0.06 7 23 (3 X l0) I6 200 2.7 0.07 8 l2 (8 X10 [6 H2 2.7 0.07

*mol density means mols of dye per liter of solution From the results shown in Table 1, it will be understood that the direct positive silver halide emulsions of this invention have high sensitivity and Dmax, and further show good clearance. Also, it will be understood the alkylated dyes among the above-indicated dyes of this invention gave direct positive silver halide emulsions having higher sensitivity (refer to Sample 2 and Sample 3). Furthermore, the dyes used in this example having the quinoline nucleus as the cyanine heterocyclic nucleus gave particularly high sensitivity.

EXAMPLE 2 The silver halide emulsion used in this example was prepared in the following manner.

To a first solution prepared by dissolving at 60C. 10g of inert gelatin and 5 cc of 1 normal aqueous sodium chloride solution in 500 cc of water were added a second solution prepared by dissolving 100 g of silver nitrate in 500 cc of water at 60C. and a third solution prepared by dissolving 35 g of sodium chloride in 300 cc of water at 60C, over a 20 minute period with stirring while maintaining the system at 60C. Thereafter, the mixture was ripened for 50 minutes at 60C and then a fourth solution prepared by dissolving 14 g of potassium bromide in 200 cc of water at 60C was added to the mixture with stirring over a 5 minute period. The resultant mixture was then further rippened for l0 minutes at 60C and, after reducing the temperature to 35C, the mixture was washed with water. The mixture was heated again, the pH thereof was adjusted to 10, hydrazine and gold chloride were added thereto in the amounts given in Example 1, and the mixture was ripened again for 10 minutes. Thereafter, the pH of the ripened mixture was adjusted to 6.5 using 8 ml of 10 wt citric acid. Furthermore, a fifth solution prepared by dissolving g of inert gelatin in 300 cc of water was added to the mixture to yield the silver halide emulsion. The mean grain size of the silver halide grains in the silver halide emulsion thus obtained was about 0.15 micron.

32 cc of a methanol solution of pinakryptol yellow in a concentration of 5 X l0 mol per liter of solution was added to the silver halide emulsion prepared above and then a methanol solution of a dye as shown in Table 2 was added to the mixture. After further adding thereto suitable amounts of mucochloric acid and saponin as in Example 1, the resultant silver halide emulsion was applied to a cellulose triacetate film in a dry thickness of about 2 microns to give a sample.

The sample prepared was exposed* through an optical wedge to a tungsten light source of 2854K and developed for 3 minutes at 20C. in the developer having the following composition. exposure time I second Composition of the developer:

water (about 30C) 50 cc anhydrous sodium sulfite 30 g p-l'ormaldehyde 7,5 g sodium bisulfite 2,2 g boric acid 7.5 g hydroquinone 22.5 g potassium bromide l.6 g water added to make I liter Table 2 Dye (mol density") cc/lOO g of Sample emulsion Sensitivity Dmax Dmin l 100 3.0 0.07 2 18 (8 X l") 8 933 2.9 0.04 3 20 (8 X l0") I6 1620 3.0 0.06 4 21 (8 X I0") 24 25! 3.0 0.07 5 22 (8 X l0") 16 282 2.9 0.06 6 23 (8 X l0") I6 282 3.0 0.07 7 l (8 X [0) l6 l32 3.0 0.07

same meaning as in Table I From the results shown in Table 2, it will be understood that the direct positive silver halide emulsions of this invention have high sensitivity, high Dmax, and good clarance.

While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What we claim is:

l. A fogged direct positive silver halide emulsion containing at least one cyanine dye comprising a pyrazolo[ l,5-a]benzimidazole nucleus and a cyanine heterocyclic nucleus, which nuclei may be substituted with substituents as are commonly used in the cyanine dye art, in which the carbon atom at the 3-position of the pyrazolol l,5-a]benzimidazole nucleus is joined to the 2-position or 4-position of the cyanine heterocylic nucleus, by a methine chain, the carbon atom being joined to the 4-position, however, only when the cyanine heterocyclic nucleus is a quinoline nucleus or a pyridine nucleus, said cyanine dye being present in a concentration effective to provide high sensitivity, maximum image density and providing substantially no color stains.

tive silver halide emulsion comprises silver halide grains fogged by a reducing agent and a gold compound.

6. A direct positive silver halide emulsion as set forth in claim 1 wherein the silver halide in the silver halide emulsion comprise regular silver halide grains having a mean grain size of 0.05 micron to 1.0 micron.

7. A direct positive silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion further contains at least one organic desensitizer.

8. A direct positive silver halide emulsion as set forth in claim 7 wherein said at least one organic desensitizer is a compound represented by the following formula wherein R represents an alkyl group or an ally] group, Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus, Xrepresents an acid anion, m represents 0, 1, or 2, and a represents 1 or 2.

9. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion further contains a color coupler for photography.

10. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine dye is a compound represented by the following formula 2. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine dye is an alkylated cyanine dye.

3. A direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is a benzathiazole nucleus, a benzaselenazole nucleus, a Z-quinoline nucleus or a 4-quinoline nucleus.

5. A direct positive silver halide emulsion as set forth in claim 1 wherein the silver halide in the direct posiwherein R represents an alkyl group, a hydroxyalkyl group, and acetoxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, an alkoxycarbonylalkyl group, a sulfoalkyl group, an aralkyl group, a sulfoaralkyl group, a carboxyalkyl group, or a vinylmethyl group; R represents a hydrogen atom, an alkyl group, a carboxyl group, an alkoxycarbonyl group, an amino group, an acylamino group, an aryl group, or an acid amide group; L and L each represents a methine chain, and L and R may be combined with each other by a meth ylene chain; Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus; n represent 0 or 1; m represents 0, 1, or 2, and p represents 1, 2, 3, or 4.

lected from the group consisting of an alkyl group, a

hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, an alkoxycarbonylwherein R and R each represents an alkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, an alkoxycarbonylalkyl group, a sulfoalkyl group, an aralkyl group, a sulfoaralkyl group, a carboxyaralkyl group, or a vinylmethyl group; R represents a hydrogen atom, an alkyl group, a carboxyl group, an alkoxycarbonyl group, an amino group, an acylamino group, an aryl group or an acid amide group; L and L each represents a methine chain, and L and R may be combined with each other by a methylene chain; R represents a halogen atom, a lower alkyl group, an alkoxyl group, an aryl group, a carboxyl group, an alkoxycarbonyl group or an acylamino group; Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus; X repre sents an acid anion; n represents or 1, m represents 0, l, or 2; and p represents 1, 2, 3, or 4.

12. A fogged direct positive silver halide photo graphic material comprising a support having therein a fogged direct positive silver halide emulsion layer, said silver halide emulsion layer containing at least one cyanine dye comprising a pyrazolo[l,5-a]benzimidazole nucleus and a cyanine heterocyclic nucleus, which nuclei may be substituted with substituents as are commonly used in the cyanine dye art, in which the carbon atom at the 3-position of the pyrazolol l ,5-a]benzimidazole nucelus is joined to the 2-position or the 4- position of the cyanine heterocyclic nucleus by a methine chain, said carbon atom being joined to the 4-position, however, only when the cyanine heterocylic nucleus is a quinoline nucleus or a pyridine nucleus, said cyanine dye being present in a concentration effective to provide high sensitivity, maximum image density and providing substantially no color stains.

13. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is substituted with a member selected from the group consisting of an alkyl group, an aryl group, an hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, a nitro group and a halogen atom.

14. A fogged direct positive silver halide emulsion as set forth in claim 13 wherein said alkyl group has 1-20 carbon atoms, said alkoxy group has l-lO carbon atoms and said aryl group is a phenyl group.

15. A fogged direct positive silver halide emulsion as set forth in claim 14 wherein said pyrazolol 1,5-albcnzimidazole nucleus is substituted with a member se alkyl group, a sulfoalkyl group, an aralkyl group, a sulfoaralkyl group, a carboxyaralkyl group, a vinylmethyl group, hydrogen, a carboxyl group, an alkoxycarbonyl group, an amino group, an acylamino group, an aryl group and an acid amide group.

16. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein in said pyrazolo[ l, 5-a]l:ien-

zimidazole nucleus:

the carbon atom at the 2-position thereof is methyl or phenyl substituted;

the benzine ring thereof is unsubstituted;

the nitrogen atom connected to the carbon atom at the 2-position thereof is unsubstituted, methyl substituted or sulfopropyl substituted.

17. A fogged direct positive silver halide emulsion as set forth in claim 13 wherein:

the carbon atom at the 2position thereof is methyl or phenyl substituted;

the benzene ring thereof is unsubstituted;

the nitrogen atom connected to the carbon atom at the 2-position thereof is unsubstituted, methyl substituted or sulfopropyl substituted.

18. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is selected from the group consisting of an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, 21 naphthothiazole nucleus, at selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a 2-pyridine nucleus, 21 4-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a 3-isoquinoline nucleus, a lisoquinoline nucleus, an imidazole nucleus, a benzimidazole nucleus, an indolenine nucleus, an imidazo[4,5- b]quinoxaline nucleus and a pyrrolidine nucleus.

19. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein the amount of said cyanine dye is l X l0 to 2 X 10 mol of dye or dyes per mol of silver halide.

20. A fogged direct positive silver halide emulsion as set forth in claim 10 wherein the amount of said cyanine dye is l X 10 to 2 X 10 mol of dye or dyes per mol of silver halide.

21. A fogged direct positive silver halide emulsion as set forth in claim 11 wherein the amount of said cyanine dye is l X 10 to 2 X 10 mol of dye or dyes per mol of silver halide.

22. A fogged direct positive silver halide photographic material as claimed in claim 12 wherein said cyanine dye is a compound represented by the follow ing formula ll N wherein R, represents an alkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, an alkoxycarbonylalkyl group, a sulfoalkyl group, an aralkyl group, a sulfoaralkyl group, a carboxyaralkyl group, or a vinylmethyl group; R represents a hydrogen atom, an alkyl group, a carboxyl group, an alkoxycarbonyl group, an amino group, an acylamino group, an aryl group, or an acid amide group; L, and L each represents a methine chain, and L, and R, may be combined with each other by a methylene chain; Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus; 11 represents O or 1; m represents 0, l, or 2, and p represents 1, 2, 3, or 4.

23. A fogged direct positive silver halide photographic material as claimed in claim 22 wherein the amount of said dye is l X l to 2 X mol of dye amino group, an acylamino group, an aryl group or an acid amide group; L, and L each represents a methine chain, and L, and R, may be combined with each other by a methylene chain; R represents a halogen atom, a lower alkyl group, an alkoxyl group, an aryl group, a carboxyl group, an alkoxycarbonyl group or an acylamino group; Z represents an atomic group necessary for forming a cyanine heterocyclic nucleus; Xrepresents an acid anion; n represents 0 or 1, m represents 0. l or 2; and p represents 1, 2, 3, or 4.

25. A fogged direct positive silver halide photographic material as set forth in claim 24 wherein the amount of said dye is l X 10 to 2 X 10 mol of dye or dyes per mol of silver halide.

26. A fogged direct positive silver halide emulsion as set forth in claim 10 wherein M is l or 2.

or y P mol of silver q 27. A fogged direct positive silver halide emulsion as 24. A fogged direct positive silver halide photo- Set forth in Claim 11 wherein M is 1 or 2 ph material as Claimed In Claim 12 wherein Said 28. A fogged direct positive silver halide photocyanme dye IS the compound represented by the folgraphic material as claimed in claim 22 wherein M is l lowing formula: or 2.

M R1-N (CH:CH C=EL1-L2==) i-Rz 29. A fogged direct positive silver halide photographic material as claimed in claim 24 wherein M is l 

1. A FOGGED DIRECT POSITIVE SILVER HALIDE EMULSION CONTAINING AT LEAST ONE CYANINE DYE COMPRISING A PYRAZOLO(1,5-A)BENZIMIDAZOLE NUCLEUS AND A CYANINE HETEROCYCLIC NUCLEUS, WHICH NUCLEI MAY BE SUBSTITUTED WITH SUBSTITUENTS AS ARE COMMONLY USED IN THE CYANINE DYE ART, IN WHICH THE CARBON ATOM AT THE 3-POSITION OF THE PYRAZOLO(1,5-A)BENZIMIDAZOLE NUCLEUS IS JOINED TO THE 2-POSITION OR 4-POSITION OF THE CYANINE HETEROCYLIC NUCLEUS, BY A METHINE CHAIN, THE CARBON ATOM BEING JOINED TO THE 4-POSITION, HOWEVER, ONLY WHEN THE CYANINE HETEROCYCLIC NUCLEUS IS A QUINOLINE NUCLEUS OR A PYRIDINE NUCLEUS, SAID CYANINE DYE BEING PRESENT IN A CONCENTRATION EFFECTIVE TO PROVIDE HIGH SENSITIVITY, MAXIMUM IMAGE DENSITY AND PROVIDING SUBSTANTIALLY NO COLOR STAINS.
 2. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine dye is an alkylated cyanine dye.
 3. A direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is a benzathiazole nucleus, a benzaselenazole nucleus, a 2-quinoline nucleus or a 4-quinoline nucleus.
 4. A direct positive silver halide emulsion as set forth in claim 1 wherein the silver halide in the direct positive silver halide emulsion comprises chemically fogged silver halide grains.
 5. A direct positive silver halide emulsion as set forth in claim 1 wherein the silver halide in the direct positive silver halide emulsion comprises silver halide grains fogged by a reducing agent and a gold compound.
 6. A direct positive silver halide emulsion as set forth in claim 1 wherein the silver halide in the silver halide emulsion comprise regular silver halide grains having a mean grain size of 0.05 micron to 1.0 micron.
 7. A direct positive silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion further contains at least one organic desensitizer.
 8. A direct positive silver halide emulsion as set forth in claim 7 wherein said at least one organic desensitizer is a compound represented by the following formula
 9. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion as set forth in claim 1 wherein said silver halide emulsion further contains a color coupler for photography.
 10. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine dye is a compound represented by the following formula
 11. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine dye is the compound represented by the following formula
 12. A fogged direct positive silver halide photographic material comprising a support having therein a fogged direct positive silver halide emulsion layer, said silver halide emulsion layer containing at least one cyanine dye comprising a pyrazolo(1,5-a)benzimidazole nucleus and a cyanine heterocyclic nucleus, which nuclei may be substituted with substituents as are commonly used in the cyanine dye art, in which the carbon atom at the 3-position of the pyrazolo(1,5-a)benzimidazole nucelus is joined to the 2-position or the 4-position of the cyanine heterocyclic nucleus by a methine chain, said carbon atom being joined to the 4-position, however, only when the cyanine heterocylic nucleus is a quinoline nucleus or a pyridine nucleus, said cyanine dye being present in a concentration effective to provide high sensitivity, maximum image density and providing substantially no color stains.
 13. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is substituted with a member selected from the group consisting of an alkyl group, an aryl group, an hydroxyl group, an alkoxyl group, a carboxyl group, an alkoxycarbonyl group, a nitro group and a halogen atom.
 14. A fogged direct positive silver halide emulsion as set forth in claim 13 wherein said alkyl group has 1-20 carbon atoms, said alkoxy group has 1-10 carbon atoms and said aryl group is a phenyl group.
 15. A fogged direct positive silver halide emulsion as set forth in claim 14 wherein said pyrazolo(1,5-a)benzimidazole nucleus is substituted with a member selected from the group consisting of an alkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an alkoxyalkyl group, a carboxyalkyl group, an alkoxycarbonylalkyl group, a sulfoalkyl group, an aralkyl group, a sulfoaralkyl group, a carboxyaralkyl group, a vinylmethyl group, hydrogen, a carboxyl group, an alkoxycarbonyl group, an amino group, an acylamino group, an aryl group and an acid amide group.
 16. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein in said pyrazolo(1,5-a)benzimidazole nucleus: the carbon atom at the 2-position thereof is methyl or phenyl substituted; the benzine ring thereof is unsubstituted; the nitrogen atom connected to the carbon atom at the 2-position thereof is unsubstituted, methyl substituted or sulfopropyl substituted.
 17. A fogged direct positive silver halide emulsion as set forth in claim 13 wherein: the carbon atom at the 2-position thereof is methyl or phenyl substituted; the benzene ring thereof is unsubstituted; the nitrogen atom connected to the carbon atom at the 2-position thereof is unsubstituted, methyl substituted or sulfopropyl substituted.
 18. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein said cyanine heterocyclic nucleus is selected from the group consisting of an oxazoline nucleus, an oxazole nucleus, a benzoxazole nucleus, a naphthoxazole nucleus, a thiazoline nucleus, a thiazole nucleus, a benzothiazole nucleus, a naphthothiazole nucleus, a selenazole nucleus, a benzoselenazole nucleus, a naphthoselenazole nucleus, a 2-pyridine nucleus, a 4-pyridine nucleus, a 2-quinoline nucleus, a 4-quinoline nucleus, a 3-isoquinoline nucleus, a 1-isoquinoline nucleus, an imidazole nucleus, a benzimidazole nucleus, an indolenine nucleus, an imidazo(4,5-b)quinoxaline nucleus and a pyrrolidine nucleus.
 19. A fogged direct positive silver halide emulsion as set forth in claim 1 wherein the amount of said cyanine dye is 1 X 10 6 to 2 X 10 2 mol of dye or dyes per mol of silver halide.
 20. A fogged direct positive silver halide emulsIon as set forth in claim 10 wherein the amount of said cyanine dye is 1 X 10 6 to 2 X 10 2 mol of dye or dyes per mol of silver halide.
 21. A fogged direct positive silver halide emulsion as set forth in claim 11 wherein the amount of said cyanine dye is 1 X 10 6 to 2 X 10 2 mol of dye or dyes per mol of silver halide.
 22. A fogged direct positive silver halide photographic material as claimed in claim 12 wherein said cyanine dye is a compound represented by the following formula
 23. A fogged direct positive silver halide photographic material as claimed in claim 22 wherein the amount of said dye is 1 X 10 6 to 2 X 10 2 mol of dye or dyes per mol of silver halide.
 24. A fogged direct positive silver halide photographic material as claimed in claim 12 wherein said cyanine dye is the compound represented by the following formula:
 25. A fogged direct positive silver halide photographic material as set forth in claim 24 wherein the amount of said dye is 1 X 10 6 to 2 X 10 2 mol of dye or dyes per mol of silver halide.
 26. A fogged direct positive silver halide emulsion as set forth in claim 10 wherein M is 1 or
 2. 27. A fogged direct positive silver halide emulsion as set forth in claim 11 wherein M is 1 or
 2. 28. A fogged direct positive silver halide photographic material as claimed in claim 22 wherein M is 1 or
 2. 29. A fogged direct positive silver halide photographic material as claimed in claim 24 wherein M is 1 or
 2. 